The ICS 3 is a constant current (CC) source that limits the necessary current to drive the light safely. Without a CC source like an ICS 3 the light would vary in brightness and could be damaged by unregulated currents. The ICS 3 is the best choice for systems that require more light than an ICS 2, and for situations that require freezing motion and reducing blur (strobe operation).
ICS 3: Uses and Application
What is the ICS 3 and why do I need it?